1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device having an electrode that penetrates a semiconductor substrate (so called a through silicon (or substrate) via: hereinafter abbreviated as “TSV”) and a manufacturing method thereof.
2. Description of the Related Art
Recently, along with the high functionality and diversification of semiconductor devices, a semiconductor device, in which a plurality of semiconductor chips is integrated through vertical stacking of the semiconductor chips, has been proposed. Such a semiconductor device is configured to achieve electrical continuity between the semiconductor chips through the TSV that penetrates a semiconductor substrate of the semiconductor chip.
Since the TSV is formed to penetrate the semiconductor substrate, it is necessary to achieve insulation between the semiconductor substrate and the TSV. Accordingly, it has been proposed to separate the TSV from a semiconductor layer of a device region through an annular insulation separation portion (that is called an insulation ring) around the TSV.
One of methods to separate the TSV from the semiconductor layer includes forming a hole for the TSV from the main surface of the semiconductor substrate, forming an insulating layer on the side wall of the hole and burying the hole which is inside of the insulating layer with a conductive material to form the TSV. In this case, the insulation ring is provided in contact with the TSV.
As another method for forming the insulation ring, there is a method for forming the insulation ring that is isolated from the TSV. In this case, an annular trench is firstly formed from the main surface of the semiconductor substrate and embeds an insulating material in the trench to form the insulation ring. Next, main surface structures including semiconductor elements are formed on the main surface of the semiconductor substrate. Thereafter the thickness of the semiconductor substrate is reduced by back surface grinding or the like so as to expose the bottom part of the insulation ring on the back surface of the semiconductor substrate. A hole for forming the TSV is formed in the region surrounded by the insulation ring from the back surface of the semiconductor substrate and a conductive material is buried in the hole to form the TSV.
The annular trench is necessary to form, for example, with a depth of 40 to 50 μm and with a width of 2 to 3 μm (aspect ratio of 13 to 25), and to additionally bury an insulating film in the trench with good coverage.
As a way to bury the insulating film in the trench, there is a CVD (Chemical Vapor Deposition) method, a SOD (Spin On Dielectric) method, or the like (for example, see JP2009-111061A).
As a CVD method with good coverage, there may be a method of forming a TEOS (tetraethoxysilane)-NSG (Non-doped Silicate Glass) film in a low pressure CVD (LPCVD) method using TEOS and additionally performing thermal densification.
Further, in order to suppress the increase of the aspect ratio of the annular trench, there has been proposed a method of forming a polysilicon film in the annular trench having a wide width with a film thickness not occluded in the trench and performing thermal oxidation on the inside thereof (see JP2008-251964A). According to the forming method of JP2008-251964A, a ring-shaped separation trench (with a width of about 5 μm) is formed in a silicon substrate, and then a polycrystalline silicon film of about 2 μm is conformally formed by the CVD method. Then, a silicon thermal oxide film with a thickness of about 0.8 μm is formed by thermal oxidation of the polycrystalline silicon film. Thereafter, a CVD silicon oxide film is formed by the CVD method to be buried in gaps (see paragraphs [0021] to [0025]). Here, in the process of forming the silicon thermal oxide film of about 0.8 μm from the polycrystalline silicon film, the silicon thermal oxide film is buried with a thickness of about 1.6 μm in accordance with wall on both sides of the trench. In typical thermal oxidation, about a half of the silicon thermal oxide film is formed on the original silicon side, and the remaining half is formed in a direction in which the original silicon is inflated. Accordingly, the gap that remains in the trench has a width of about 200 nm, and the CVD silicon oxide film is buried in the gap.
The CVD silicon oxide film is usually subjected to a thermal densification after deposition and thus thermally-densified CVD silicon oxide film tends to act a tensile stress in the depth direction of the surrounding silicon substrate due to volume shrinkage. If such a CVD silicon oxide film is buried in the whole trench, as illustrated in FIG. 1(a), it has been found that the substrate surrounding the insulation ring may be collapsed by the tensile stress.
On the other hand, the silicon thermal oxide film, which is buried in the trench through oxidation of the silicon by the thermal oxidation method, tends to act a compressive stress in the depth direction of the surrounding silicon substrate by volume expansion. If most of the insulation ring is formed by such a silicon thermal oxide film, as illustrated in FIG. 1(b), the substrate surrounding the insulation ring may be uplifted by the compressive stress. These phenomena may occur, not limited to the case of the insulation ring that is isolated from the TSV, even in a case of the insulation ring formed in contact with the TSV.
As described above, according to the method of forming the insulation ring in the related art, the silicon substrate surrounding the insulation ring may be deformed. Since the insulation ring is provided to achieve electrical insulation between the TSV and the device area, the device area is formed on the outside of the insulation ring, and the TSV is formed on the inside of the insulation ring. Once the silicon substrate surrounding the insulation ring is deformed, the device area on the outside and/or the TSV on the inside may not be properly formed. Accordingly, such deformation of the silicon substrate causes the decrease of production yield.